import java.util.Scanner;
public class Eight {
	public static void main(String[] args) {
		Scanner reader = new Scanner(System.in);
		int x1 = reader.nextInt();
		int y1 = reader.nextInt();
		int x2 = reader.nextInt();
		int y2 = reader.nextInt();
		Point p1 = new Point(x1, y1);	 //传入第一个坐标
		Point p2 = new Point(x2, y2);	 //传入第二个坐标
		double m = Point.Distance(p1, p2);	 //调用Point的Distance方法计算距离
		System.out.printf("%.2f", m);	//格式化输出
	}
}
class Point {
	double x;
	double y;
	public Point(double x, double y) {
		this.x = x;
		this.y = y;
	}
	public static double Distance(Point a, Point b) {
		double i = Math.pow((a.x - b.x), 2);     //计算横坐标相减的平方和
		double j = Math.pow((a.y - b.y), 2);     //计算纵坐标相减的平方和
		return Math.sqrt(i + j);	  //开根号
	}
}
